Lost weight and FIV

Hi
I have a FIV cat, he is 9 years old. He was quite big, 14 pounds, but he lost a lot of weight in the last 4 months. The thing is, he still eat as much as before, even if he have bad teeth. He have always have a big apetite and a little anxiety toward empty bowl... Otherwise he is his old self, playing and cuddling. My vet found nothing else wrong related to his FIV -except his usual eyes problem- so I am not sure what to do. Can FIV cause lost of weight even with a good quality food in apropriate quantity?